Introduction
The reaction process of oxy-anion as an oxidizing agent is very complicated and gives rise to various intermediates and products. Ardon and Plane I have found that the oxidation reaction of chromium(II) leads to different chromium(Ill) products depending on whether a one-or two-electron oxidation step occurs. With a typical one-electron oxidizing agent such as chlorine a chromium(Ill) product is monomeric Cr 3 +, and with a two-electron one such as oxygen only a chromium(III) dimer is obtained. In the case of chlorate ion, 70~o of chromium(III) product is in the dimeric form, showing that chlorate ion acts as both one-and two-electron oxidizing agent to chromium(II). Further investigation for this system has been performed by Thompson and Gordon 2, indicating that two chromium(II) are oxidized by way of successive one-electron oxidation steps.
For our present purpose, a metal ion which has various oxidation states is desirable to distinguish which type of the oxidation steps occurs. Vanadium ion is suitable for clarifying this problem because of its various oxidation states and the strong reducing ability of vanadium(II). It is polarographically anomalous that the reduction potential of vanadium(IV) to vanadium(II) (--~-0.9 V vs. SCE) is more negative than that of vanadium(Ill) to vanadium(II) ( ~-0 . 5 V vs. SCE) 3. This makes it possible to detect vanadium(III) as a reaction product by its reduction current. We attempted to investigate the oxidation reaction of vanadium(II) with chlorate ion and nitrite ion by a polarographic method. If the reaction proceeds only by way of a two-electron oxidation step, the product of metal ion which differs by two units of oxidation state appears and then reacts with an initial metal ion to yield the product which has the same oxidation state as that formed by way of a one-electron oxidation step. Before this primary product is consumed by the subsequent reaction, it is necessary to identify the oxidation state of the product for the elucidation of the oxidation mechanism. An electrochemical technique is available for the detection of the product: metal ion in low oxidation state can be easily produced and, in the presence of oxidizing agent, follows the homogeneous oxidation reaction at the vicinity of the electrode surface;' hence it is possible to detect immediately and directly the primary product by measuring the electrolytic current. Kalousek's polarography 4' 5 is the most useful for this purpose. Applying this method to the catalytic current of chlorate ion with vanadium(II), it has been found that chlorate ion acts mainly as a one-